Mixer amplifiers are essential components for all transmitters and receivers operating at radio frequencies (RF) and are used in most communication systems. In particular, mixer amplifiers are used in cellular telephone and other types of telecommunication sets to transpose the frequency of a signal without modifying the information that it conveys.
In particular, on transmission, the mixers are used to transpose radio frequencies to a useful signal to be transmitted and delivered at an intermediate frequency. Conversely, in reception, mixers are used to transpose the RF frequency of a received signal to a relatively low intermediate frequency in order to be able to be processed by downstream electronic circuits.
Thus, two conventional operating modes can be distinguished for the mixer, on one hand in the uplink direction on transmission, which corresponds to the transposition of the frequency of the signal being processed from the intermediate frequency FI to the high frequencies and, on the other hand, in the downlink direction on reception, which corresponds to the transposition of the RF frequency to the intermediate frequency (FI). Currently, there are various types of mixer amplifiers that can be used to obtain such behaviour.
Conventional active circuits for producing front-end circuits are advantageous because they can be used to obtain a very compact integration. Conventional active circuits, however, exhibit relatively mediocre noise and linearity performance characteristics. In particular, the mixer requires, on reception, high performance characteristics in terms of linearity and noise.
In this respect, the second order linearity of a mixer amplifier, which is defined by the point of interception of the tangent of the input power at the first harmonic with the tangent of the input power at the second harmonic, in their linear zones, and which qualifies the spectral purity of the mixer amplifier, is a parameter that must be mastered.